JP3462041B2 - X-ray diagnostic equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct conversion system X.
The present invention relates to the structure of a line diagnostic device.

[0002]

2. Description of the Related Art Conventionally, an X-ray diagnostic apparatus is a useful apparatus capable of nondestructively inspecting a specimen, and it is desired that a moving image can be obtained with high definition. Further, in order to avoid making the device large and heavy, a flat detector of the diagnostic device is required. In order to achieve these requirements, an active matrix type flat panel detector has been proposed. There are an indirect conversion method and a direct conversion method in such a flat panel detector, but the direct conversion method can obtain a higher definition image than the indirect conversion method. This direct conversion method is, for example, EIDuPont
USP5319206 and DLLee et al. SPIE vol.2432 p.23
7 known in 1995, and will be described with reference to FIGS. 13 (a) and 13 (b). First, the X-ray X incident on the photoconductor 301 is
Electron / hole pairs 309 are generated, and the generated charges generate the signal capacitance 305 and the electrode 300 facing the pixel electrode 304.
And the capacity formed by and. The charge incident on the X-ray is collected in the integrator through the drains D1 to D4 when the gate G of the transistor is opened by the signal from the gate signal Gl. In the direct conversion method, the photoconductor 301
Since all the information incident on is collected as electron-hole pairs 309, it is possible to realize a high-definition image by refining the pixel electrode shape. Where 308
Is a power source, and the insulating film 302 is a film for preventing circuit breakdown due to abnormal increase in the potential of the pixel electrode 304 because a large amount of electron-hole pairs 309 are also generated at the same time when the X-ray dose is large. is there. The capacitance formed by the insulating film 302 becomes the protective capacitance 312 on the equivalent circuit. The newly provided protective capacitor 312 has an effect of mitigating a potential rise due to charges corresponding to electron-hole pairs generated by X-ray irradiation. Therefore, destruction of the transistor 306 and the signal capacitor 305 can be prevented.

However, this conventional method has a drawback that it cannot support moving images. This is especially true for Figure 13 (b)
The equivalent circuit will be described. The charges generated by the X-rays are distributed to the protective capacitance 312, the capacitance of the pixel electrode 304 of the photoconductor, and the signal capacitance 305. By opening the gate G of the transistor 306, the charges of the signal capacitor 305 and the photoconductor capacitor 304 can be read using the data line D. The signal reading operation can initialize the signal capacitance 305 and the photoconductor capacitance 304. At this time, in order to initialize the charge of the protective capacitor 312, it takes time corresponding to a time constant depending on the internal resistance of the photoconductor 301 and the resistance of the transistor 306. Therefore, this method has a problem that even if it is possible to achieve high definition, it is impossible to obtain a moving image, which is a unique problem in the direct method.

[0004]

In the method using the conventional direct conversion method, a high-definition image can be obtained but the moving image cannot be obtained. The present invention provides an X-ray diagnostic apparatus capable of obtaining a high-definition image and a moving image without impairing the advantage of the direct conversion method for preventing the element destruction due to the voltage rise of the pixel potential in the X-ray diagnostic apparatus. To aim.

[0005]

In order to solve the above-mentioned problems, the present invention provides a photoconductor having two main surfaces facing each other for generating carriers by X-ray irradiation, and one of the photoconductors. A pixel electrode formed on the main surface side for receiving the carrier, a signal capacitor connected between the pixel electrode and a power supply potential, for receiving the carrier and accumulating a detected charge corresponding to the carrier, and a signal capacitor connected to the signal capacitor. An X-ray diagnostic apparatus comprising: a first transistor that detects the electric charge as a pixel potential; and an active element that is connected to the signal capacitor and releases a part of the detected electric charge to the power supply potential. provide.

The active element is a second transistor which has an offset region between the source / drain electrode and the gate electrode and has a higher breakdown voltage than the first transistor, and is arranged from the gate electrode in the offset region. It is possible to set the amount of the partial charge by the distance between the source and drain electrodes.

Further, according to the present invention, a plurality of Xs arranged two-dimensionally are arranged.
A plurality of pairs of a line light receiving element and the X-ray light receiving element are formed, and a plurality of pixel capacitors are formed in a pair in the pixel capacitor and a pixel capacitor for accumulating charges generated from the X-ray light receiving element, and a source is connected to the pixel capacitor. And a plurality of signal capacitors connected between the source of each of the first transistors and the power supply potential, and a first transistor for extracting the charge accumulated in the pixel capacitor as a detection signal from the drain according to the timing of opening the gate. And an active element connected between a terminal for accumulating the electric charge of the pixel capacitor and a power supply potential and releasing a part of the electric charge to the power supply potential when the terminal exceeds a certain potential. Provided is an X-ray diagnostic apparatus.

Here, the active element may be a second transistor having a source and a drain connected to both ends of the signal capacitor. The gate electrodes of the second transistors may be commonly connected. The power supply potential includes not only positive and negative power supply potentials but also GND.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In order to prevent the pixel potential from abnormally rising due to X-ray irradiation, the present invention is designed such that an active element such as a high voltage transistor (particularly a thin film transistor (TFT)).
The essence is to provide a charge storage circuit configuration and a circuit configuration for initialization. This will be described in detail using the following examples.

(Embodiment 1) An embodiment of the present invention will be described with reference to FIG. FIG. 1A is a sectional structural view of an embodiment of the present invention, and FIG. 1B is an equivalent circuit diagram of one pixel. The electrode 100 and the pixel electrode (the pixel capacitor 104 is formed by these two electrodes so as to sandwich the photoconductor 101 from above and below).
Since the charges used are the charges accumulated in the pixel electrode 104, the pixel capacitors and the pixel electrodes are given the same numbers) 10
4 are formed. The following circuit configuration for reading the signal charges is formed for the pixel electrode 104. The first transistor 10 is connected in parallel with the signal capacitor 105. Further, the second transistor 106 is connected to the pixel electrode. D, D1, D2, etc. indicate signal lines or connections with signal lines. Here, in the present invention, it is important that the first transistor 10 is of a high breakdown voltage type. Hereafter, the first transistor 10 will be referred to as a high breakdown voltage transistor.

The operation principle of this embodiment will be described with reference to FIG. 1B, which is an equivalent circuit for one pixel. By the X-ray irradiation, the pixel capacitor 104 and the signal capacitor 10 in the photoconductor 101 portion are
The signal charge is distributed to 5. As a result, the pixel potential (point A) rises. At this time, the high breakdown voltage transistor 10
An appropriate constant gate voltage is applied to the gate line 110b of the second transistor 10b to turn it on, and the second transistor 10
6. Operate so as to release a part of the accumulated charges so that the breakdown voltage is not applied to the signal capacitor 105. Further, when the electric charge in the signal capacitor 105 is read, the unnecessary electric charge is not stored anywhere, so the initialization is easy. Therefore, it is possible to avoid the circuit destruction of the transistor 106 and the like due to the rise of the pixel potential, which is a problem in the direct conversion method, and further, the initialization can be realized in a sufficiently short time, so that an X-ray diagnostic apparatus capable of outputting a moving image can be obtained. You can

The reason why the high breakdown voltage transistor 10 is required will be described with reference to FIG. FIG. 2 shows a comparison between the voltage-current characteristic 20 of a normal transistor and the voltage-current characteristic 21 of a high breakdown voltage transistor. The high breakdown voltage transistor has a drain current I in a region where the drain voltage Vd is small.
d hardly flows. However, there is a certain drain voltage Vdo
The characteristic is that a large drain current Id is observed with the threshold value as. The high breakdown voltage transistor described with reference to FIG. 1 needs to have the characteristics as shown in FIG. Therefore, the drain voltage Vdo is set to the signal capacitance 1 described in FIG.
05 and the pixel capacitor 104 withstand voltage or less, the role described in FIG. 1 can be fulfilled.

Next, the cross-sectional structure of the X-ray diagnostic apparatus of the present invention using the structure of the high breakdown voltage transistor will be described to explain that the drain voltage Vdo can be arbitrarily set. FIG. 3 shows a cross-sectional structure of one pixel of the X-ray diagnostic apparatus of this embodiment.
An electrode 100 and a pixel electrode 104 are arranged on both ends of the photoconductor 101. Further, a signal capacitor 105 having a pair of the pixel electrode 104 and the electrode 112 is formed, and a transistor 106 for reading a signal charge and a high breakdown voltage transistor 1 are formed on both sides of the signal capacitor 105.
0 is formed. In the signal charge reading transistor 106, the gate electrode 107 is formed on the substrate 115, and the semiconductor electrode 108 is sandwiched between the drain electrode of the high breakdown voltage transistor 10 and the electrode 114 which also serves as the source electrode of the signal charge reading transistor 106, and the drain electrode 109. It has a staggered structure. The high breakdown voltage transistor 10 also has an inverted stagger structure. The high withstand voltage transistor 10 has a gate electrode 111, which is connected to a gate line of a system different from the gate electrode of the transistor 106 for reading the signal charge. Transistor 10 for signal reading
6 is bilaterally symmetric, whereas high breakdown voltage transistor 10
Is an offset region Lo at the contact portion with the gate electrode 111.
The feature is that ff is formed. Offset area Lo
ff means the contact layer 113 from the end of the gate electrode 111.
And the distance to the contact B of the semiconductor layer 108. The drain voltage Vdo described in FIG. 2 can be arbitrarily set by the offset length Loff. In this embodiment, the offset region Loff is set to the drain electrode 114, which is likely to have a high potential, but the same effect can be expected if it is set to the source electrode 119 side. Further, the same effect can be expected regardless of whether the source or drain is set. Next, the manufacturing process will be specifically described with reference to FIG. First, the electrode patterns 107, 111, and 112 are processed and formed on the insulating substrate 115 by, for example, a sputtering method, whole-surface resist coating and mask patterning, etching and the like. A transparent insulating substrate such as a glass substrate may be used as the insulating substrate 115. The electrode patterns 107 and 111 are also gate electrodes of the transistor, and 112 is an electrode of a signal capacitor described later. In this sense, the electrodes 107, 111, 112
Is desired to have low resistance, and Mo, Ta, W, Al, C
u or an alloy containing at least one of these metals may be used. The film thickness of the electrodes 107, 111, 112 is 50 nm to 30
A thickness of 0 nm is desirable from the viewpoint of realizing the low resistance described above and at the same time improving the coverage of the first insulating film described later. Patterned electrodes 107, 111, 11
The first insulating film 116, the semiconductor layer 108, and the second insulating film 117 are deposited on the second insulating film 116. For film formation, a film formed by chemical vapor deposition (PECVD) by plasma excitation is used in consideration of film deposition on a large area. PECVD
Using a silicon oxide film as the first insulating film 116,
A silicon nitride film, a silicon oxynitride film, or a stacked film thereof is deposited, hydrogenated amorphous silicon is deposited as the semiconductor layer 108, and a silicon oxide film, a silicon nitride film, or a silicon oxide film is deposited as the second insulating film. A nitride film or a laminated film of these may be deposited. The semiconductor layer 108 is
It may be polycrystalline silicon, microcrystalline silicon, or the like. The film thickness of the first insulating film 116 is the same as the above-mentioned electrodes 107, 111, 1
12 and 100 n so that a sufficiently large electric field can be applied to the semiconductor 108 to obtain a sufficient on / off ratio of the transistor to be produced.
The thickness of the semiconductor layer 108 is 20 nm to 300 nm in order to secure a sufficient volume velocity per unit time and the on / off ratio of the transistor, and the thickness of the second insulating film 117 is the source / drain. The thickness may be 100 nm to 400 nm in order to obtain a sufficient margin when etching the contact layer 113 to form an electrode (FIG. 4A).

Next, the second insulating film 117 is patterned and the contact layer 118 is deposited. Contact layer 1
N + type amorphous silicon doped with P or the like was used as 18. Besides this, n + type polycrystalline silicon, microcrystalline silicon, or the like can be used. Contact layer 118
The film thickness may be 20 nm to 300 nm. Second insulating film 11
7 is a pattern for determining the channel length of the transistor. Particularly, in the high breakdown voltage transistor 10 in FIG. 3, it is also a pattern for determining the offset length Loff. The offset length Loff is a value that should be determined by the pixel potential that rises according to the X-ray detection efficiency. In addition, the offset length Loff is determined due to the constraint of the pattern alignment accuracy in the manufacturing process. From this point of view, it is desirable that the offset length Loff is 2 μm or more in order to make the withstand voltage of the obtained high breakdown voltage transistor sufficient and to avoid a short circuit between patterns (FIG. 4B).

After that, the source / drain electrode layer 114 is deposited. Al as the source / drain electrode layer 114,
A good source / drain electrode layer 114 can be formed by using Mo, an alloy thereof, or a laminated film. The thickness of the source / drain electrode layer 114 may be 300 nm to 1 μm in order to obtain a sufficiently low resistance wiring (FIG. 4).
(C)).

Further, the source / drain electrode layer 114 is patterned, and the contact layer 113 is patterned using the patterned source / drain electrode layer 114 as a mask, whereby the source / drain electrodes 109, 114, 1 are formed.
19 is formed (FIG. 4D).

Further, an interlayer insulating film 219 is deposited on each completed transistor, and etching is performed so that the source / drain electrodes 114 are exposed in order to form a signal capacitance with the electrode 105. As the interlayer insulating film 219, the above-described PECVD may be used, and a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film thereof may be used. If the film thickness is 300 nm to 1 μm, it is good in terms of insulation and stability of characteristics (FIG. 5 (a)).

Next, the pixel electrode 10 is formed so as to fill this hole.
4 is formed. A transparent conductive film, such as Indi
um Tin Oxide may be used, or a metal thin film such as Al may be used. The pixel electrode 104 may have a film thickness of 100 nm to 500 nm. Further, an X-ray detecting photoconductor 101 is deposited on the pixel electrode 104, and the electrode 100 is formed so as to face the pixel electrode 104. Amorphous selenium or amorphous silicon may be used as the photoconductor 101, and the film thickness is 10
If it is set to 0 μm to 1 mm, it is good in terms of X-ray conversion efficiency. The electrode 100 may be made of Al or the like, and the film thickness may be about 100 nm (FIG. 5B).

In this way, the X-ray detector is formed on the pixel electrode 104, and the signal capacitor 105, the signal charge reading transistor 106 and the high breakdown voltage transistor 10 can be obtained.

FIG. 6A shows an equivalent circuit in which the detector portion for one pixel shown in FIG. 1 is two-dimensionally arranged. It will be described that a two-dimensional X-ray diagnostic diagram is obtained using this diagram. It is assumed that the signal charge Q11 is accumulated by the X-ray irradiation in the signal capacitor 105 connected to the gate line G1 and the data line D1. Signal charge Q11 is large and signal capacity is 1
When the breakdown voltage of 05 and the breakdown voltage of the charge reading transistor 106 are reached, the high breakdown voltage transistor 10 discharges along the path (a). Next, when reading Q11, a voltage is applied to the gate line G1 and the transistor 106 is opened, so that the charge Q11 passes through the path (b).
To the readout amplifier 600 or charge integrator. In this way, the pixel signal corresponding to the pixel potential dropped from the breakdown voltage can be detected. At this time, charges of all pixels connected to the gate line G1, for example, Q
12, Q13 ... Are similarly read. After a sufficient time elapses in this way, the voltage of the gate line G1 is turned off, then the gate line G2 is turned on, and the charges, Q21, Q22, Q23, ... After selecting all the gate lines, can get a 2D image. The gate electrodes of the high breakdown voltage transistors 10 arranged in the row direction in the detector have g1, g2, g3 ,.
As shown in FIG. 6A, the common potential is applied through the gate lines of ... To prevent a high voltage from being applied to the signal capacitance. Here, the method of applying the gate voltage to the first transistor 106 and the high breakdown voltage transistor 105 is based on different systems, but it may be used at the same potential as the source electrode of the first transistor 106. That is, as shown in FIG. 6B, the gate potential and the drain potential of the high breakdown voltage transistor are short-circuited. By doing so, not only the number of wirings can be significantly reduced, which is advantageous in yield, but also the power for switching the high breakdown voltage transistor 10 can be reduced. This potential and the offset length Loff described with reference to FIG. 6A can prevent the destructive voltage rise of the pixel potential, and at the same time, the charge of the signal capacitor 105 can be instantly initialized. Further, the resolution of the obtained two-dimensional image depends only on the pixel area. In this sense, the configuration of the present invention makes it possible to obtain a high-definition moving image, which has not been obtained in the past.

In the X-ray diagnostic apparatus of the direct conversion system for directly detecting the electron-hole pairs generated by X-ray irradiation, the signal capacity for accumulating the signal charges of X-ray irradiation is constituted by the configuration of the above embodiment. By providing a high voltage transistor in parallel, the signal capacitance, the transistor for reading the signal charge, and the X-ray detection unit are prevented from being electrically destroyed, and the signal capacitance is initialized by reading the signal charge. You can As a result, it became possible to obtain high-definition moving images by the direct conversion method. In addition, without using complicated wiring configuration and without changing the manufacturing process of the conventional detector at all, only by changing the pattern, a high-definition moving image that could not be obtained in the past can be realized with the X-ray diagnostic apparatus. can do.

(Second Embodiment) A second embodiment will be described with reference to FIGS. 7 and 8.
Will be explained. The difference from the first embodiment is the structure of the transistor and the like, and the other points are the same, and therefore the description will focus on this transistor. FIG. 7 is an equivalent circuit for explaining the second embodiment. A signal reading transistor 706 is connected to the gate line G and the data line D, and the signal reading transistor 706 has a signal capacitance 705 and an X-ray detection unit 711.
And a detector capacitance 704 are connected. Signal capacity 705
The source and drain of the high breakdown voltage transistor 710 are connected to both ends of, and the source electrode is dropped to the ground potential.

The signal charge reading transistor 706 is a high breakdown voltage transistor having an offset structure like the high breakdown voltage transistor 710, and the offset region of the signal charge reading transistor 706 is provided on the signal capacitance 705 side. The circuit configuration is as follows.

FIG. 8 shows a sectional structure for one pixel corresponding to FIG. An offset (offset amount Loff) of the signal charge reading transistor 706 is centered around the signal capacitance 705.
The 1) side and the offset (offset amount Loff2) side of the high breakdown voltage transistor 710 are formed so as to face each other. Electrode 80
7 is the gate line G in FIG. 7, the electrode 809 is the data line D in FIG. 7, and the pixel electrode 804 and the electrode 812 are the signal capacitors 7 in FIG.
Configure 05. Electrode 800 so as to sandwich photoconductor 801
The pixel electrode 804 configures the X-ray detection unit 711 and the detection unit capacitor 704 in FIG. 7.

The manufacturing process is the same as that of the first embodiment, but the feature is that the structure of the signal charge reading transistor 706 has an offset Loff1 as shown in FIG. It can be realized simply by changing the pattern.

In the second embodiment, compared with the case where the signal charge reading transistor 706 is a normal transistor shown in the first embodiment, the pixel electrode and the data line of the signal charge reading transistor 706 generated at the time of X-ray detection. The withstand voltage against the potential difference is improved. The signal charge reading transistor 706 has a role of quickly transferring the charge of the signal capacitor 705 to the data line D. Therefore, not only must the breakdown voltage with respect to the pixel potential be increased, but also a sufficient drain current must be obtained. Therefore, the offset length Loff1 of the signal reading transistor 806 is
1011 is an offset length L of the high breakdown voltage transistor 810.
It is desirable that the relation of off2 1012 is Loff1 <Loff2. In addition to the effect similar to that of the first embodiment, this embodiment also has an effect that it is possible to prevent the breakdown of the signal charge reading transistor 706 by the high potential generated at the point A. Therefore,
It is important that the point A side of the signal reading transistor 706 is offset.

(Third Embodiment) This embodiment is different from the first embodiment in the structure of two transistors, and is otherwise the same as the first embodiment. Example 3 will be described with reference to FIG. FIG. 9 shows a sectional structure for one pixel. Example 2
As shown by, two transistors are connected around the signal capacity 905. One of the two transistors is the signal charge reading transistor 906, and the other is the high breakdown voltage transistor 910 shown in the first and second embodiments. Transistor 906 for signal reading
And the high breakdown voltage transistor 910 both have an offset structure, and the offset region is formed on the signal capacitance side.
Further, the two semiconductor layers 908 are characterized in that they are not isolated. Regarding other configurations, the same parts as in Example 1 are shown in the 900 series with the last two digits being the same number. By having such a structure, in addition to having the same effect as that of the first embodiment, the insulation resistance of the signal capacitor 905 is increased, and when the charge generated by X-ray irradiation is accumulated in the pixel and the pixel potential increases, It can prevent destruction. The manufacturing process is the same as in the first and second embodiments, and can be easily realized by changing the patterning shape of the semiconductor layer 908. In addition to the effect similar to that of the first embodiment, this embodiment can reduce the area occupied by the two or more transistors 906 and 910 by bringing them closer to each other in order to prevent element isolation. This is possible, and there is an effect that high definition of the X-ray diagnostic apparatus can be realized.

(Embodiment 4) An embodiment relating to the structure of the transistor having the offset shown in Embodiment 1, Embodiment 2 and Embodiment 3 will be described. Since the other points than the transistor structure are the same as those in the first embodiment, the description thereof will be omitted.

When the transistor having the offset is applied to the X-ray diagnostic apparatus, its role is to read the signal charge and initialize the charge of the signal capacitance. FIG. 10 shows an embodiment of a transistor structure for making these two compatible. In a transistor having a gate electrode 1007, a gate insulating film 1016, a semiconductor layer 1008, a second insulating film 1020, a contact layer 1013, and a source / drain electrode 1009 on an insulating substrate 1015, an offset length Loff is formed. In addition, the second insulating film 102
A length Lov is formed on 0 so as to cover the source / drain electrode 1009.

Here, the offset length is the distance from the end of the gate electrode to the point where the semiconductor layer 1008 and the contact layer 1013 are in contact, or the end of the second insulating film. Lov is the distance from the electrode pattern end of the source / drain electrode to the end of the second insulating film. In the transistor structure described above, there is provided a transistor characterized in that the relationship between the offset lengths Loff and Lov is Loff <Lov.

The operational characteristics of the transistor shown in FIG. 10 will be described. Carriers flowing in the transistor are generated by the potential of the gate electrode 1007. Gate electrode 1007
In the offset region deviating from the above, the amount of carriers is not adjusted by the gate electrode 1007, and reaches the drain electrode 1208 only according to the potentials of the end of the gate electrode 1007 and the drain electrode 1208. It is difficult to flow. Parasitic capacitance between the drain electrode 1208 and the gate electrode 1007 is also generated, and in this sense, it is suitable for use in the high breakdown voltage transistor 10 shown in FIG. 3 of the first embodiment.

However, in order to quickly suppress the pixel potential to the breakdown voltage or less when the pixel potential rises, it is necessary for the carriers to flow better when the pixel potential rises. Drain electrode 1 in the offset region of the transistor shown in FIG.
By setting 208 to be the same as the pixel electrode potential, the pixel potential can be suppressed to the breakdown voltage or lower without increasing the voltage resistance and the leak current.

The drain electrode 1 is formed on the second insulating film 1020.
Reference numeral 208 denotes the semiconductor layer 100 sandwiching the second insulating film 1020.
8 and a MOS structure. Therefore, by connecting the pixel electrode potential and the drain electrode 1208 and raising the pixel electrode potential more than that, the drain electrode 1208 forms a channel in the semiconductor layer 1008 immediately below, and excess charges can be released. As the excess charge is released, the pixel electrode potential, that is, the drain electrode 1208 potential also decreases, and the channel is closed.

In this way, by setting the drain electrode shape in the offset region to Lov> Loff, it is possible to more efficiently realize the dual roles of controlling the potential of the high breakdown voltage transistor and retaining charges of the signal capacitor. In addition to the effect similar to that of the first embodiment, this embodiment can increase the on-current of the transistor in the on-state, and the charge at point A in FIG. 1B can be efficiently released. It also has the additional effect of being able to.

(Embodiment 5) An embodiment relating to the structure of the transistor having the offset shown in Embodiment 1, Embodiment 2 and Embodiment 3 will be described.

FIG. 11 shows a sectional structure of the transistor structure of the fifth embodiment. Since the other points than the transistor structure are the same as those in the first embodiment, the description thereof will be omitted. A light-shielding film 1302 is formed over an insulating substrate 1301, and a gate electrode 1304 is formed with an interlayer insulating film 1303 therebetween. Gate insulating film 1305, semiconductor layer 1306, second
This is a transistor structure having an insulating film 1307, a contact layer 1308, and source / drain electrodes 1309.

In the transistor structure described above, the second
The pattern of the insulating film 1307 plays an important role. First
The pattern of the second insulating film 1307 determines the channel length and offset length of the transistor. In this sense, the second
It can be said that the insulating film 1307 is a pattern that determines the transistor characteristics.

When such transistors are two-dimensionally arranged in a large area like an X-ray diagnostic apparatus, it is important that the transistor characteristics are uniform within the effective area. Figure 11
Provides a method of forming the second insulating film in a self-aligned manner in order to improve the uniformity of characteristics. The light-shielding film 1302 on the insulating substrate 1301 and the gate electrode 1304 are characterized by having an overlapping region.

A method of forming the second insulating film 1307 in a self-aligned manner will be described with reference to FIG. Insulating substrate 140
A light-shielding film 1402 is formed by patterning on
A gate electrode 1404 is formed through the interlayer insulating film 1403. Next, a gate insulating film 1405, a semiconductor layer 1406, and a second insulating film 1407 which are films included in a transistor are sequentially deposited. A photoresist 1408 is applied to pattern the second insulating film 1408. When patterning the photoresist 1408,
Without using ordinary mask exposure, a photoresist 1408 for patterning the second insulating film 1407 in a self-aligned manner is exposed from the back side of the insulating substrate 1401 using the light shielding film 1402 and the gate electrode 1404 as a mask. By adopting such a method, the second insulating film 1407 has the same effect as that of the first embodiment according to this embodiment, and the second insulating film 1407 has a misalignment by a self-aligning method as shown in FIG. There will be no formation. Therefore, it is possible to ensure the uniformity of the transistor characteristics for controlling one pixel of the X-ray diagnostic apparatus that requires a two-dimensional image.

[0040]

With the above structure, the X-ray diagnostic apparatus can obtain a high-definition image and a moving image without impairing the advantage of the direct conversion system for preventing the element destruction due to the voltage rise of the pixel potential in the X-ray diagnostic apparatus. Can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an X-ray diagnostic apparatus according to a first embodiment of the present invention and an equivalent circuit diagram for one pixel.

FIG. 2 is a diagram for explaining the first embodiment of the present invention.

FIG. 3 is a pixel cross-sectional view of Embodiment 1 of the present invention.

FIG. 4 is a cross-sectional view in the order of manufacturing steps according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional view in the order of manufacturing steps according to the first embodiment of the present invention.

FIG. 6 is an operation explanatory diagram when the pixels according to the first embodiment of the present invention are arranged two-dimensionally.

FIG. 7 is an equivalent circuit diagram of a second embodiment of the present invention.

FIG. 8 is a sectional view showing a pixel structure according to a second embodiment of the present invention.

FIG. 9 is a sectional view showing a pixel structure according to a third embodiment of the present invention.

FIG. 10 is a cross-sectional view and an operation principle explanatory diagram of a fourth embodiment of the present invention.

FIG. 11 is a pixel cross-sectional view of Example 5 of the present invention.

FIG. 12 is a diagram for explaining the fifth embodiment of the present invention.

FIG. 13 is an example of a conventional direct conversion type X-ray diagnostic apparatus.

[Explanation of symbols]

10 First transistor 100 electrodes 101 photoconductor 104 pixel electrode 105 Signal capacity 106 second transistor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H01L 27/14 H01L 27/14 K 27/146 C (56) References JP 10-10237 (JP, A) JP JP 10-284713 (JP, A) Tokuyo HEI 8-509550 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 5/32 H01L 27/14 A61B 6/00-6 / 14 G01T 1/00-7/12

Claims (5)

(57) [Claims] A photoconductor to 1. A generating carriers by X-ray irradiation has two opposing major surfaces, and a pixel electrode for receiving the carrier is formed on one main surface of the photoconductor, the pixel is connected between the electrodes and the power source potential, and the signal capacity for accumulating charges detected corresponding to the carrier receiving said carrier, a first transistor to detect connected the charge to the signal capacitance as pixel potential, the signal An X-ray diagnostic apparatus comprising: an active element connected to a capacitor to release a part of the detected charge to the power supply potential. 2. The active element includes source / drain electrodes.
Has an offset region between the gate electrode and a first of the second transistor with high withstand voltage than a transistor, the part by the distance between the source and drain electrodes from the gate electrode in the offset region The X-ray diagnostic apparatus according to claim 1, wherein the amount of electric charge of the X-ray is set . A plurality of X-ray receiving element arranged wherein two-dimensional, X-ray formed a plurality of the light receiving element and the pair, a pixel capacitor for storing charge generated from the X-ray receiving element, a pair in the pixel capacitance in a plurality of formed, wherein that source is connected to the pixel capacitor, a first transistor retrieving the pixel capacitor to the charges accumulated in accordance with the timing gate is opened as a detection signal from the drain, said first transistor respectively the source of the a plurality of signal capacitor connected between the power supply potential, the power supply potential portion of the charge when the connected between the terminals and the power supply potential for storing charge the terminal exceeds a predetermined potential of the pixel capacitor An X-ray diagnostic apparatus comprising: 4. The X-ray diagnostic apparatus according to claim 3, wherein the active element is a second transistor having a source and a drain connected to both ends of the signal capacitor. 5. The X-ray diagnostic apparatus according to claim 4 , wherein the gate electrodes of the second transistors are commonly connected.